Accurate IP address verification...
Each numeric part of an IP address must be between 0 and 255. All patterns I have seen on the net cover this range but they allow leading zeros. The valid cases are:
* 0
* 1, 10-19 and 100-199 aka 1[0-9]{0,2}
* 2 and 20-29 aka 2[0-9]?
* 200-249 aka 2[0-4][0-9]
* 250-255 aka 25[0-5]
* 3-9 and 30-99 aka [3-9][0-9]?

Accurate Canadian postal code format verification.
The format of a Canadian postal code is LDL DLD where L are alpha characters and D are numeric digits. But there are some exceptions. The letters D, F, I, O, Q and U never appear in a postal code because of their visual similarity to 0, E, 1, 0, 0, and V respectively. In addition to avoiding the six &quot;forbidden&quot; letters W and Z also do not appear as the first letter of a postal code (at least not at present).

Accurate UK postal code format verification.
UK postal codes have two parts. The right part is formatted as DLL (L:letter D:digit) and the left part has six alternative formats: LD, LDL, LDD, LLD, LLDL and LLDD. There is only one exception to these formats: GIR 0AA.